Controlled composting procedures have been proposed over the past for the purpose of providing an improved disposal of municipal refuse, sewage, sludge, plant waste and similar biodegradable materials. The advantages attendant with this form of treatment are manyfold, for instance, the compost or end product of the procedures not only represents a significant reduction in waste volume, thereby minimizing land-fill disposal needs, but also, may represent a product of significant commercial value as a carrier, inert or otherwise, for a wide variety of products including fertilizers and the like.
Certain of the digestive systems heretofore proposed look to multi-phase procedures of decompositions. For instance, in one arrangement, as disclosed in U.S. Pat. No. 2,820,703, the waste materials are caused to undergo a fungal mold action, following which a period which decomposition is predominantly carried out by bacteria active in a mesophilic phase at temperatures below 45.degree.-50.degree. C. is effected. Generally following such phase, a period of maximum biodegradation is permitted to ensue wherein bacteria in the thermophilic phase at temperatures about 45.degree.-50.degree. C. are witnessed. These multi-phase techniques for waste decomposition, have been observed to exhibit numerous disadvantages when considered for use in most installations. In this regard, more elaborate plant facilitites are required, pathogens and the like are present in the noted preliminary digestive phases which lead to health control problems. Further, objectionable odors are witnessed.
Proposals for overcoming these disadvantages through the utilization of systems operating only in the thermophilic phase and temperature range have been propagated, see for instance U.S. Pat. Nos. 3,010,801; 3,138,448 and 3,285,732 by Schulze.
The effective maintenance of the thermophilic phase of digestion on scales considered practical for municipal disposal systems however, have proved to be an involved and difficult undertaking. Not only is it necessary to assure proper growth of thermophilic bacteria through maintenance of requisite incubation temperatures, but also the biochemical oxygen demand (BOD) of the system must be accommodated for as well as such related pre-digestion process parameters as moisture control, optimum particle size formation and the like. Failure of the system to accomodate for any of these parameters results in an output product which is unacceptable both by reason of the failure of a complete digestion thereof as well as by the opportunity for the carrying therewithin of pathogenic materials to render the output useless for further practical or commercial utilization. Typical of the digestive systems proposed to accommodate the manyfold difficulties associated with large scale waste digestive installations are those described in Pierson, U.S. Pat. No. 3,523,012 or Hardy, U.S. Pat. No. 3,114,622. Generally, the difficulties encountered in the development of the systems heretofore proposed appear to have involved a failure of meeting the biochemical oxygen demand of the digestive process, failure to maintain necessary temperatures to achieve thermophilic phase decomposition as well as failure to derive a practical arrangement for developing and maintaining that waste matter water content considered optimum to achieve proper digestion.